JM3851012801BGA Datasheet, PDF (6/12 Pages) Analog Devices – Pin Programmable, Precision Voltage Reference

AD584
Data Sheet
THEORY OF OPERATION
APPLYING THE AD584
With power applied to Pin 8 and Pin 4 and all other pins open,
the AD584 produces a buffered nominal 10.0 V output between
Pin 1 and Pin 4 (see Figure 3). The stabilized output voltage can
be reduced to 7.5 V, 5.0 V, or 2.5 V by connecting the programming
pins as shown in Table 4.
Table 4.
Output
Voltage (V)
7.5
5.0
2.5
Pin Programming
Join the 2.5 V (Pin 3) and 5.0 V (Pin 2) pins.
Connect the 5.0 V pin (Pin 2) to the output pin (Pin 1).
Connect the 2.5 V pin (Pin 3) to the output pin (Pin 1).
The options shown in Table 4 are available without the use of any
additional components. Multiple outputs using only one AD584
can be provided by buffering each voltage programming pin
with a unity-gain, noninverting op amp.
V_SUPPLY
8
AD584
10V
V_OUT
1.215V
1
24kΩ
5V
*
2
12kΩ
2.5V
3
6kΩ
V_BG
6
6kΩ
R4
R1
R3
R2
COMMON 4
approximately 20 V, even for the large values of R1. Do not
omit R2; choose its value to limit the output to a value that can
be tolerated by the load circuits. If R2 is zero, adjusting R1 to its
lower limit results in a loss of control over the output voltage.
When precision voltages are set at levels other than the standard
outputs, account for the 20% absolute tolerance in the internal
resistor ladder.
Alternatively, the output voltage can be raised by loading the
2.5 V tap with R3 alone. The output voltage can be lowered by
connecting R4 alone. Either of these resistors can be a fixed
resistor selected by test or an adjustable resistor. In all cases, the
resistors should have a low temperature coefficient to match the
AD584 internal resistors, which have a negative temperature
coefficient less than 60 ppm/°C. If both R3 and R4 are used,
these resistors should have matching temperature coefficients.
When only small adjustments or trims are required, the circuit
in Figure 4 offers better resolution over a limited trim range. The
circuit can be programmed to 5.0 V, 7.5 V, or 10 V, and it can be
adjusted by means of R1 over a range of about ±200 mV. To trim
the 2.5 V output option, R2 (see Figure 4) can be reconnected to
the band gap reference (Pin 6). In this configuration, limit the
adjustment to ±100 mV to avoid affecting the performance of
the AD584.
V+
8
10.0V
1
AD584
5.0V
2
2.5V
3
6 ^VBG
V_OUT
R2
300kΩ
R1
10kΩ
* THE 2.5V TAP IS USED INTERNALLY AS A BIAS POINT
AND SHOULD NOT BE CHANGED BY MORE THAN 100mV
IN ANY TRIM CONFIGURATION.
Figure 3. Variable Output Options
The AD584 can also be programmed over a wide range of output
voltages, including voltages greater than 10 V, by the addition
of one or more external resistors. Figure 3 illustrates the general
adjustment procedure, with approximate values given for the
internal resistors of the AD584. The AD584 may be modeled
as an op amp with a noninverting feedback connection, driven
by a high stability 1.215 V band gap reference (see Figure 5 for
schematic).
When the feedback ratio is adjusted with external resistors, the
output amplifier can be made to multiply the reference voltage
by almost any convenient amount, making popular outputs of
10.24 V, 5.12 V, 2.56 V, or 6.3 V easy to obtain. The most general
adjustment (which gives the greatest range and poorest resolution)
uses R1 and R2 alone (see Figure 3). As R1 is adjusted to its upper
limit, the 2.5V pin (Pin 3) is connected to the output, which
reduces to 2.5 V. As R1 is adjusted to its lower limit, the output
voltage rises to a value limited by R2. For example, if R2 is
approximately 6 kΩ, the upper limit of the output range is
4
COMMON
Figure 4. Output Trimming
R40
Q10
C52
C51 _Q6
R41
Q20
Q11
Q12
Q14
Q16
Q13
SUB
V+
Q7 _STROBE
Q8
Q15 ^R42
R34
R37
Q5
R35
OUT 10V
5V TAP
2.5V TAP
CAP
C50
R33 R32
Q3 Q4
R38
Q2
V_BG
R30
Q1
R39
R31
R36
V–
Figure 5. Schematic Diagram
Rev. C | Page 6 of 12